Charging method of electrophotographic materials

ABSTRACT

A charging method for an electrophotographic material comprising a highly insulating support and a photoconductive insulating coating thereon, which comprises subjecting a first region of the photoconductive coating to a first corona discharge of one polarity while simultaneously irradiating with light, whereby said irradiation is absorbed by said photoconductive coating, and at the same time subjecting a second region of said photoconductive coating which is continuous to and radiation insulated from said first region, to a second corona discharge of the opposite polarity and causing a relative movement between said electrophotographic material and the corona discharge devices in such a manner that said electrophotographic material is subjected to said first corona with light irradiation and then is subjected to said second corona successively, is disclosed.

United States Patent [1 1 Sato et al.

[ 1 Dec. 11, 1973 CHARGING METHOD OF ELECTROPHOTOGRAPHIC MATERIALS [73] Assignee: Fuji Photo Film Co., Ltd.,

Kanagawa, Japan [22] Filed: Aug. 18, 1972 [21] Appl. No.: 281,927

[30] Foreign Application Priority Data Aug. 20, 1971 Japan 46/63430 [52] US. Cl. 250/325, 317/262 A [51] Int. Cl 603g 13/02 [58] Field of Search 96/1 R, l'C; 250/495 ZC; 317/262 A [56] References Cited UNITED STATES PATENTS 2,955,938 10/1960 Steinhilper 96/1 3,676,117 7/1972 Kinoshita 96/1 Primary ExaminerWilliam F. Lindquist AltorneyGerald J. Ferguson Jr. et al.

[57] ABSTRACT A charging method for an electrophotographic material comprising a highly insulating support and a photoconductive insulating coating thereon, which comprises subjecting a first region of the photoconductive coating to a first corona discharge of one polarity while simultaneously irradiating with light, whereby said irradiation is absorbed by said photoconductive coating, and at the same time subjecting a second region of said photoconductive coating which is continuous to and radiation insulated from said first region, to a second corona discharge of the opposite polarity and causing a relative movement between said electrophotographic material and the corona discharge devices in such a manner that said electrophotographic material is subjected to said first corona with light irradiation and then is subjected to said second corona successively, is disclosed.

3 Claims, 3 Drawing Figures CHARGING METHOD OF ELECTROPI-IOTOGRAPHIC MATERIALS BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a charging method of an electrophotographic material which comprises a photoconductive coating directly provided on a high insulating support.

An electrophotographic coating directly provided on an insulating support can be electrostatically charged with a high uniformity by a method in which the coating is subjected to simultaneous corona discharging of positive and negative polarities at adjacent regions whereby the current flow is aided by a uniform irradiation of light onto the first region of the coating where the first corona discharge is carried out. The coating is ultimately charged in the polarity equal to that of the second corona discharge.

2. Description of the Prior Art An electrophotographic material having a support with a comparatively high resistance such as paper may be charged by the so called double corona method.

However, this method of charging is not applicable for materials having highly insulating supports such as polyethylene terephthalate, polyethylene, polypropylene, polycarbonate, polyamide, polyimide, polyvinyl chlorode, diand triacetyl cellulose, etc. Accordingly, a thin conductive intermediate layer is required which may be formed, for example, by the vacuum deposition of metal. In this case a photoconductive coating is formed on such a conductive layer and the coating is charged by the usual corona charging means whereby the conductive thin layer is grounded.

Electrophotographic materials which comprise a highly insulating support and a photoconductive coating directly provided thereon can be charged by a method described in British Pat. No. 971,281. In this method, the photoconductive coating is irradiated from the support side with light which is strongly absorbed by the coating to make the bottom portion contiguous to the support temporarily conductive.

A corona discharge is carried out from the frontside of the material while the bottom portion of the coating remains conductive and is grounded. This method has the limitation that the support material must be optically transparent and moreover it is accompanied with probability of incomplete grounding of the bottom portion of the coating. In addition, a conductive tip must be brought into firm contact with the photoconductive surface for the purpose of grounding and it sometimes mechanically damages the coating.

An object of the present invention is to provide a charging method of an electrophotographic material comprising a highly insulating support and a photoconductive insulating coating directly provided thereon, overcoming the above-cited shortcomings.

SUMMARY OF THE INVENTION The present method comprises, subjecting a first region of an electrophotographic coating to a first corona discharge of one polarity with a simultaneous irradiation of light, and at the same time subjecting a second region, which is continuous to and irradiation insulated or shielded, i.e., by a light shielding plate from the first region to a second corona discharge of the opposite polarity, and causing a relative movement between the electrophotographic sheet and the corona discharge devices in such a manner that the electrophotographic sheet will first accept the first corona with light irradiation and then the second corona, successively.

BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS FIG. 1 is a schematic cross-sectional view of an apparatus to carry out and to disclose the principle of the present invention.

FIG. 2 is another embodiment for carrying out the invention.

FIG. 3 is still another example of a charging apparatus to carry out the invention.

In these figures the same numbers are used in each of the figures to designate parts or materials as follows: 1; An electrophotographic material.

11; The support of the material.

12; The photoconductive insulating coating.

3; The main corona charging electrode.

4; The light source.

5; The auxiliary corona charging electrode. 51; The shield case also working as a reflector. 6; The light shielding plate.

7; The insulating carrying plate.

DETAILED DESCRIPTION OF THE INVENTION The principle on which the present method is based will be explained by reference to FIG. 1, in which an electrophotographic material 1 comprises a highly insulating support 11 and a photoconductive insulating coating 12 provided thereon. The photoconductive insulating coating may comprise, for example, a vacuum deposited amorphous selenium layer, an organic photoconductor, homogeneous mixtures of photoconductive powders (zinc oxide, cadmium sulfide) and insulating resins, etc. Suitable examples of the insulating resins include a copolymer of vinylchloride and vinyl acetate, a copolymer of styrene and butadiene, a copolymer of styrene and butyl methacrylate, polyalkyl methacrylates, polyalkyl acrylates, polyvinyl acetate, polyvinyl butyral, alkyd resins, silicone resins, epoxy resins, epoxy ester resins, as well as copolymers, terpolymers or quadripolymers of (l) a vinyl monomer having hydroxy groups capable of reacting with an isocyanate and (2) a monomer such as styrene, an alkyl methacrylate or an alkyl acrylate, cross-linked with polyisocyanates, and an alkyd or epoxy ester cross-linked with polyisocyanates. Suitable examples of the insulating support include polyethylene terephthalate, triacetyl cellulose, diacetylcellulose, polyethylene, vinyl chloride and vinylidene chloride films and paper or metals laminated thereon with the above plastic films. Above the material is a charging device, which comprises a main corona discharge electrode 3, a shield case 31 for 3, a light source 4, an auxiliary corona discharge electrode 5, a shield case 51 for 5 which also acts as a light reflector, and a light shielding plate 6 having a thickness of about 0.1 to 1 mm. The plate may be made of conductive or insulating material.

For the purposes of illustration only the hereinafter explanation will be given for the case where the photoconductive insulating coating 12 exhibits the n-type semiconductive performance.

A negative high potential is applied to the main corona electrode 3, and a positive high potential is applied to the auxiliary electrode 5, respectively whereby the photoconductive coating 12 is uniformly irradiated by light using the light source 4 which activates the photoconductive coating and does not coat too strong memory in it.

Electrons abundantly present in the exposed area A are repelled by the negatively charged corona ions generated from the electrode 3 and attracted to the positive corona ions impinging onto the region A and finally neutralized there. Thus an accumulation of positive charges results at the boundary region between the exposed and unexposed regions. n the other hand, negative charges deposited on the surface of the unexposed region forms an electric double layer together with the accumulated positive charges.

When the electrophotographic material 1 is transported in the direction shown by the arrow, the material is uniformly charged in a negative polarity. This method is also suitable for those materials which exhibit a photoconductive memory effect by irradiation prior to charging.

FIG. 2 illustrated a schematic cross sectional view of a specific apparatus to carry out the present invention.

In this embodiment, the light shielding plate employed in the device shown in FIG. 1 is replaced by a shield case for a corona electrode 5. In addition this case not only forms a part of a light reflector 51 but also it forms a part of the shield case 31 for a main corona electrode 3. A roll of an electrophotographic material is fed continuously into the apparatus to be charged.

Some examples to illustrate the present invention in greater detail will be shown below.

Example 1 'A photoconductive selenium coating of about micron thickness was vacuum deposited on a 150 micron thick polyethylene terephthalate film which had been irradiated with ultra-violet light to improve the surface adhesive properties. The electrophotographic material thus prepared was subjected to charging with an apparatus as shown in FIG. 3. The material 1 was placed on a non-plasticized polyvinyl chloride plate 7 of 10 mm in thickness.

A light shielding plate 6 was placed perpendicular to the material surface with one mm clearance between the lower end of the plate and the surface. The plate was made of metal with 0.5 mm thickness and electrically isolated from the surroundings. Separated by the plate 6, two needle-shaped electrode 3 and 5, perpendicular to the surface to the material 1 were provided. The distance from the plate 6 to each needle was 50 mm. The electrode 3 was kept at +8 KV, while 5 was kept at 8 RV. A 100 W incandescent lamp 4 was provided near the electrode 5, and at a distance of 300 mm to the surface to be charged. When the lamp was put on, the polyvinyl chloride plate 7 bearing the material 1 was transported at a rate of l cm/sec in the direction shown by the arrow. The material 1 showed a surface potential of 250 volts immediately after being passed under the main corona electrode 3.

Example 11.

On a 150 mm micron thick polyethylene terephthalate film was coated a mixture comprising 100 parts by weight of a photoconductive zinc oxide, trade name Sazex No. 2000," 14 parts by weight of a resin binder, a styrenated alkyd resin produced by Japan Reichhold Chemical Co., under the trade name Styresol No. 4400, 7 parts by weight of polyisocyanate compound as a curing agent for the alkyd resin, produced by Bayer A.G. under the trade name Desmodur L to give a dried coating thickness of about 7 microns. The coated film was kept at 40 C for 16 hours to complete the curing. A charging apparatus having the same arrangement and structure as described in Example 1 was employed to charge the film thus prepared. The light shielding plate 6 was made of a 1 mm thick black nonplasticized polyvinyl chloride board. The clearance between the end of the board and the film surface was about 1' mm, the distance from the incandescent lamp to the film surface was 200 mm, and the polarities of the electric potential applied to the two electrodes were reversed, i.e., -8 KV to the main corona electrode 3, and +8 KV to the auxiliary one 5. The film was kept stationary under the arrangement for about 5 seconds, when a surface potential -l40 volts was observed in about a 2 mm width narrow band along the lower end of the light-shielding board 6. When the film was transported in the direction shown by the arrow, a wide area of the photoconductive surface could be uniformly charged.

In the present method, irradiation of the photoconductive insulating layer is required to be carried out in a manner in which the layer is temporarily made conductive. It is not desirable to cause too strong a memory effect for photoconductivity in the layer, because it results in a reduction in the ultimate surface potential of the layer such a consideration of strong memory must be given when the photoconductive layer in which photoconductive powder is dispersed in resin is used. From this point of view, it is desirable to use a filter which absorbs a particular spectral range of light which causes an intensive memory effect. For instance, an ultra-violet light absorbing filter is preferably employed when a zinc oxide layer is used. Together with the filter, the light sources must be taken into account. When zinc oxide is dispersed in the resin, satisfactory results can be obtained by cutting the wavelength shorter than 390 mu.

While the invention has been described in detail and in terms of specific embodiments thereof, it will be apparent to one skilled in the art that various changes and modifications can be made therein without departing from the spirit and scope thereof.

What is claimed is:

l. A method for charging an electrophotographic material consisting of a highly insulating support for a photoconductive insulating coating having majority carriers of a predetermined polarity, which comprises providing a first corona discharge device of a first polarity opposite to said predetermined polarity and a light source, providing a second corona discharge device of a polarity opposite to said first polarity, said first and second corona discharge devices being the only discharge devices, real or imaginary, provided, providing a shielding member between said light source and said second corona discharge, subjecting a first region of the photoconductive coating to said first corona discharge device while simultaneously irradiating with light from said light source whereby said irradiation is absorbed by said photoconductive coating, and at the same time subjecting a second region of said photoconductive coating which is immediately adjacent and continuous to said first region and radiation insulated therefrom by said shielding member to said second corona discharge device and causing a relative movement between said electrophotographic material and the cosisting of an amorphous selenium layer, an organic photoconductor, and a homogeneous mixture of inorganic photoconductive powders with an insulating resin.

3. The method of claim 1 wherein said photoconductive insulating coating is n-type. 

1. A method for charging an electrophotographic material consisting of a highly insulating support for a photoconductive insulating coating having majority carriers of a predetermined polarity, which comprises providing a first corona discharge device of a first polarity opposite to said predetermined polarity and a light source, providing a second corona discharge device of a polarity opposite to said first polarity, said first and second corona discharge devices being the only discharge devices, real or imaginary, provided, providing a shielding member between said light source and said second corona discharge, subjecting a first region of the photoconductive coating to said first corona discharge device while simultaneously irradiating with light from said light source whereby said irradiation is absorbed by said photoconductive coating, and at the same time subjecting a second region of said photoconductive coating which is immediately adjacent and continuous to said first region and radiation insulated therefrom by said shielding member to said second corona discharge device and causing a relative movement between said electrophotographic material and the corona discharge devices in such a manner that said electrophotographic material is subjected to said first corona with light irradiation and then is subjected to said second corona successively.
 2. The method of claim 1 wherein said photoconductive insualting coating is selected from the group consisting of an amorphous selenium layer, an organic photoconductor, and a homogeneous mixture of inorganic photoconductive powders with an insulating resin.
 3. The method of claim 1 wherein said photoconductive insulating coating is n-type. 